1. Technical Field
The present invention relates to an orthosis for stretching tissue in the human body to regain joint motion and eliminate tissue contracture. In particular, the present invention relates to an orthosis which limits compressive forces on the soft tissue around a joint while it stretches tissue around a joint. The present invention also relates to a continuous passive motion system for joint therapy.
2. Description of the Prior Art
When the full range of movement of a joint is not available, such as after surgery or trauma, tissue around the joint stiffens and loses its ability to move through the extremes of motion. Various devices have been designed to regain range of motion.
U.S. Pat. No. 4,612,919 shows an adjustable limb support for adjustably orienting the forearm and upper arm of a human patient in a variety of angular relationships to therapeutically treat the contracted muscles in the patient's arm.
U.S. Pat. No. 4,848,326 shows a knee contracture correction device for straightening a contracted knee.
U.S. Pat. No. 4,538,600 shows an adjustable splint assembly with a lower strut and an upper strut pivotably connected to the lower strut. An internal spring applies a force at the pivot point to align the upper and lower struts to straighten the limb to which the splint is attached. A similar device is also shown in U.S. Pat. No. 4,508,111. Similar devices are in use and are sold under the trademark DYNASPLINT by Dynasplint Systems, Inc.
U.S. Pat. No. 4,665,905 shows a dynamic elbow and knee extension device with a centrally positioned compression spring.
It is also known in the art to put a rigid element including a turnbuckle, on the inside angle of a joint, between two cuffs attached to limb segments and use the turnbuckle to vary the length of the rigid element to pull and push the limb segments relative to each other. If has been found that this device does not work very well in practice because it is cumbersome and difficult to obtain relatively full extension or flexion at the extremes of motion.
Each of the above-identified prior art devices, and each of the devices in use at the present time, does not apply adequate force in the appropriate planes. Further, each of these devices applies undesirable compressive forces on the soft tissues around a joint upon flexion and extension of the joint. None allows the patient to provide the proper therapy by himself, without the assistance of a therapist who manually stretches the joint. None allows the patient to control the therapy process in a self-directed manner.
Accordingly, it is desirable to provide a self-directed therapy device which not only enhances the range of motion of the joint but also limits compressive joint forces, distracts the joint and stretches soft tissue. "Distraction" is defined by one dictionary as "Separation of the surfaces of a joint by extension without injury or dislocation of the parts." (Taber's Cyclopedic Medical Dictionary, 16th Edition, 1989, page 521), and involves stretching rather than compressing the joint capsule, soft tissue, ligaments, and tendons.
The device should limit tissue damage by controlling the amount of force applied, and should apply a progressive gradual stretching action and have a locking mechanism to maintain a joint in a selected position, because tissue is viscoelastic. This is the best way to establish or reestablish a range of motion in the soft tissues around a joint, as it does not involve damaging the tissue.
An orthosis should also be lightweight and portable so that it can be used in a seated, upright, or functional position. This should be the case for both a stretching device and a continuous passive motion (CPM) device.